Roof structures of industrial buildings typically comprise roof or rafter beams which extend parallel to one another across the building in one direction and purlins mounted on the rafters which extend parallel to one another in directions normal to the rafters. Insulation material is spread in long sheets or strips over the purlins with the lengths of the sheets extending normal to the lengths of the purlins, and hard roofing material is attached to the purlins through the insulating material. In the past, roof structures of this type have been difficult to assemble, and since the seams of abutting sheets of insulating material are usually exposed to the inside of the building structure, any gaps appearing in the seams are exposed within the building structure and air within the building contacts the hard roofing material, causing heat loss and vapor condensation.
The typical construction process for a roof structure includes the steps of unreeling sheets of insulation material from large reels of insulation material and placing the sheets of material with their lengths extending across the lengths of the purlins. The sheets of insulation material are stretched to prevent sagging between the purlins, and the hard roofing material is then placed over the insulation material and connected to the purlins. The hard roofing material is used as the working surface for the workmen and the reels of insulation material are unwound on this working surface and then moved by hand over to the exposed purlins adjacent the hard roofing material. With this procedure, poor alignment of the sheets of insulation material is likely to occur and gaps between adjacent sheets of insulation material are likely to be formed.
Because of the likelihood of gaps occurring between the adjacent sheets of insulation material, some manufacturers have produced insulation material with tapes that overhang the edges of the insulation material and which would normally overlap an adjacent sheet of insulation material in the roof structure. Also, rolls of tape, glue, and other devices have been developed for connecting together the abutting edges of insulation material in a roof structure to prevent gaps from appearing between adjacent strips of material. However, it is expensive and onerous for the workmen to seal the gaps with the use of these devices. Furthermore, since the strips of insulation material must be stretched to prevent sagging between the purlins, the workmen usually extend the strips of insulation material beyond the edges of the building structure so as to leave enough material available for the workmen to pull on and to stretch the material. After the strips of insulation material have been stretched, the overhanging edge portions must be cut away and discarded as waste.
As the typical roof structure is formed, it is customary to form the entire width of the roof structure at one time, proceeding along the length of the structure from one end to the other. This method of construction has been desirable since the insulation material comes in strips or long sheets and it has been convenient for the workmen to place the long sheets across the lengths of the purlins and immediately place the hard roofing material over the insulation material in their progression along the lengths of the purlins; however, the workmen are required to move back and forth across the width of the building and carry and retrieve their various manual and electrically actuated tools with them. Furthermore, the long lengths of insulation material are difficult to handle as it is being unreeled from its reels and moved onto the purlins from the surface of the hard roofing material. While the long sheets of insulation material are difficult to handle on a still day, they are extremely difficult to handle on a windy day-- so much so that it is virtually impossible to handle the material. Of course, the wind factor also effects the neatness of the job, the number of gaps in the seams of the insulation material, the warping or stretching of the material, the number of workmen required to lay the material, and the safety of the workmen.
As set forth in U.S. Pat. No. 3,559,914, I have developed an improved roof structure and a system for applying insulation to the structure wherein the reels of insulation material are supported by adjacent ones of the purlins and the insulation material is paid out from the reels along the purlins instead of across the purlins. The insulation material spans the spaces between adjacent ones of the purlins and the edges of the strips of material extend along the upper surfaces of the purlins and are hidden from view. Support frames are provided for holding the reels of insulation material on the purlins and the support frames are pushed along the length of the purlins progressively across the roof structure as the sheets of hard roofing material are applied to the roof structure.
While my new system has met with substantial commercial success, there is also a need for heavily insulated roof structures in colder climates. When the thickness of the insulation material between the purlins and the hard roofing surface is increased, the hard roofing material tends to "work" with respect to the purlins and insulation material as the hard roofing material expands and contracts due to increases and decreases in its temperature, and as it moves in response to wind forces. Moreover, as the thickness of the insulation material between the purlins and the hard roofing surface increases, it is more difficult to attach the hard roofing surface to the purlins through the insulation material.